1. Field of the Invention
The present invention relates to an enduction type stop and holding system and offers an induction type positioning system which is suitable for employment in various kind of automatic control systems, physical distribution systems and material carrying systems.
2. Description of the Prior Art
Within the application field of this invention, a positioning system is provided to stop and hold such condition of a movable part at a specified position.
For example, the stop position in a movable body positioning system for a linear motor car has been determined by a friction brake utilizing mechanical friction generated between the movable part, namely the movable body, and the guide rail which guides the movable body.
However, the system of this type results in the following problems:
1. a complicated braking mechanism including a friction plate is necessary,
2. the stop position of the movable part changes due to the changes in the friction of the friction plate,
3. the friction heat adversly effects the mechnical part and
4. friction results in smell, smoke and noise, because the stop position is determined by the friction force through the mechanical contact between the movable part and guide rail. Particularly, such problems result in notable inconvenience for employment of such a system into office equipment.
Thus, in order to solve such disadvantages, it has been proposed to determine the stop position of the movable part while keeping the non-contact condition and without utilizing the friction force of mechanical contact.
In one method, when the movable part reaches the specified stop position, a first travelling magnetic field generation coil provided in a side of the guide rail generates a travelling magnetic field in the opposite direction to the travelling direction of the movable part, and meanwhile a second travelling magnetic field generation coil provided in the side of the guide rail generates a travelling magnetic field in the opposite direction to the direction of the travelling magnetic field generated by the first travelling magnetic field generation coil. Namely, the stop position is determined by applying the equal travelling magnetic fields on the travelling movable part in mutually opposite directions. (This method is disclosed, for example, in the material entitled "The Engineer in Wonderland", E. R. LAITHWAITE, 1967.)
However, this method also has the following disadvantages. First, it is very delicate and difficult to select the timing of applying the two travelling magnetic fields to the movable material. Second, the forces generated by the two travelling magnetic fields must strictly be equal. Third, it is not the only necessary to design the magnetic circuit in order to obtain the equal forces of the travelling magnetic fields but also the forces may easily be unbalanced due to an external factor. Fourth, the current must always be supplied to the two coils while the movable part is being held at the stop position and therefore a large amount of power is consumed making uneconomical the operation. Fifth, the movable part is likely to vibrate between the two coils and in such a case the movable part is not in a stationary condition. Sixth, the structure is inevitably complicated.